export class ContainerFocusHandler {
  private focusedIndex = 0;

  constructor(
    private getItemsCount: () => number,
    private readonly setFocusAt: (number) => void,
    private circular = false,
  ) {}

  private noItems = (): boolean => this.getItemsCount() === 0;

  private constrainFocusedIndex(): void {
    const itemsCount = this.getItemsCount();
    if (this.focusedIndex < 0) {
      this.focusedIndex = this.circular ? itemsCount - 1 : 0;
    }

    if (this.focusedIndex >= itemsCount) {
      this.focusedIndex = this.circular ? 0 : itemsCount - 1;
    }
  }

  public getFocusedIndex(): number {
    return this.focusedIndex;
  }

  public syncFocusedIndex(withCurrentIndex: number) {
    this.focusedIndex = withCurrentIndex;
  }

  public movePrevious(): void {
    if (this.noItems()) {
      return;
    }

    this.focusedIndex -= 1;
    this.constrainFocusedIndex();

    this.setFocusAt(this.focusedIndex);
  }

  public moveNext(): void {
    if (this.noItems()) {
      return;
    }

    this.focusedIndex += 1;
    this.constrainFocusedIndex();

    this.setFocusAt(this.focusedIndex);
  }

  public moveFirst(): void {
    if (this.noItems()) {
      return;
    }

    this.focusedIndex = 0;
    this.setFocusAt(this.focusedIndex);
  }

  public moveLast(): void {
    if (this.noItems()) {
      return;
    }

    this.focusedIndex = this.getItemsCount() - 1;
    this.setFocusAt(this.focusedIndex);
  }
}